"sg Ii Upgrade The Device Harmonic Conversion Unit Crystal Offline Debugging System Design

The harmonic generator is an important part of the Inertial Confinement Fusion (ICF) laser facility. The efficiency and stability of the harmonic generator is affected by the laser's quality, the crystal's quality and the precision of crystal alignment adjusting. The crystal alignment adjusting means adjust the crystals to the best angle of phase matching which should be controlled accurately in the harmonic generation.Many pulses of the main laser facility are needed for the crystal alignment adjusting online. So it's necessary to adjust the crystal alignment offline first for it work efficiency online. The basic process of the adjusting offline is shown as follow, measure the harmonic generation efficiency at different detuned angle by scanning the crystal with Nd:YLF probe laser, then fit the dates with multinomial function, draw a rocking curve and decide the best angle for the harmonic generation. It needs high precision of mechanism, collimation and thermal control. This paper studies the crystal alignment adjusting and it contains several parts as follows:(1) The optical uniformity of KDP crystals which affects the efficiency of harmonic generation has been researched. The optical uniformity of KDP crystals includes the uniformity of refractive indices, the uniformity of surface figure and the uniformity of thickness. The phase matching uniformity can be mapped by scanning the crystal's every spatial location when the precision of crystal adjusting is high enough.(2) The Crystal Alignment Verification Equipment (CAVE) which was developed for National Ignition Facility (NIF) has been researched. The design idea, optical path and the precision analysis of CAVE are studied as a good reference for the design of crystal aliment adjusting system of SG-Ⅱ.(3) A precision and automatic crystal alignment adjusting system for SG-ⅡUpgrade Project has been designed. It has an accuracy of±30μrad in phase matching angle measurement, and 4% in conversion energy measurement.(4) A crystal alignment adjusting scheme based on the current equipments we have was designed. In the experiments, the crystal alignment could be adjusted and the dates could be dealt with automatically in the system. And it has an accuracy of±50μrad in phase matching angle measurement.